There has been a doped fiber amplifier as a type of optical amplifier. Upon inputting pumping light into a doped fiber amplifier, signal light which propagates through the doped fiber amplifier is amplified. Also, a distribution Raman amplifier is another optical amplifier. A distribution Raman amplifier that controls the driving state of a Raman pumping light source, based on monitor values of an optical signal-to-noise ratio (OSNR) for wavelength division multiplexing (WDM) light channels. For example, see Japanese Laid-open Patent Publication No. 2010-122548.